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This frequency, divided by 2 16 (the largest divisor the 8253 is capable of) produces the ≈18.2 Hz timer interrupt used in MS-DOS and related operating systems. In the original IBM PCs, Counter 0 is used to generate a timekeeping interrupt. Counter 1 is used to trigger the refresh of DRAM memory. Counter 2 is used to generate tones via the PC ...
The Intel 8253 PIT was the original timing device used on IBM PC compatibles. It used a 1.193182 MHz clock signal (one third of the color burst frequency used by NTSC, one twelfth of the system clock crystal oscillator, [1] therefore one quarter of the 4.77 MHz CPU clock) and contains three timers.
The clock rate of the PC's programmable interval timer which drives the speaker is fixed at 1,193,180 Hz, [3] and the product of the audio sample rate times the maximum DAC value must equal this. Typically, a 6-bit DAC [8] with a maximum value of 63 is used at a sample rate of 18,939.4 Hz, producing poor but recognizable audio. [9]
For a list of current programs, see List of Mac software. Third-party databases include VersionTracker , MacUpdate and iUseThis . Since a list like this might grow too big and become unmanageable, this list is confined to those programs for which a Wikipedia article exists.
The aperiodic interrupts offered by the APIC timer are used by the Linux kernel tickless kernel feature. This optional but default feature is new with 2.6.18. When enabled on a computer with an APIC timer, the kernel does not use the 8253 programmable interval timer for timekeeping. [12]
The references to two timers is not true. In Intel ICH4 documentation, the timer exists in IO ports 40h..43h, and the same timer is aliased to IO ports 50h..53h for some reason. A very good guess would be that the original IBM PC had it like this too to simplify IO address decoding, but this is just a guess.
The High Precision Event Timer (HPET) is a hardware timer available in modern x86-compatible personal computers. Compared to older types of timers available in the x86 architecture, HPET allows more efficient processing of highly timing-sensitive applications, such as multimedia playback and OS task switching .
Introduced June 5, 2007, adding code samples for data compression, new video codec support, support for 64-bit applications on Mac OS X, support for Windows Vista, and new functions for ray-tracing and rendering. Version 6.1 was released with the Intel C++ Compiler on June 28, 2009. Update 1 for version 6.1 was released on July 28, 2009.